1. Field of the Invention
The present invention relates to an image-forming member for electrophotography and a manufacturing method for the same.
2. Description of the Prior Art
Generally, as a photoconductor employed for electrophotography are known an inorganic photoconductive material such as selenium dispersed in binder which is provided on a conductive substrate, an organic photoconductive material such as poly-N-vinylcarbazole, trinitrofluorenone, or azo pigment dispersed in binder which is provided on a conductive substrate, an amorphous silicon material dispersed in binder which is provided on a conductive substrate, and the like.
Electrophotographic technology is one of image formation methods. In the electrophotographic technology, a surface of a photoconductor for electrophotography receives in a dark environment electric charges generated by, for example, corona discharge. Then the photoconductor is exposed to light and electric charges only on the portion directed by light rays are selectively neutralized, whereby electrostatic latent image is formed on the photoconductor. The latent image is then developed to a visible image by the selective attraction of electroscopic fine particles (toner) consisting of colorant such as dye or pigment and binder such as macromolecule substances.
Basic properties of a photoconductor required in such a method of electrophotography are:
1) capability of receiving sufficient electric charges in a dark environment;
2) capability of holding the electric charges in a dark environment with little dissipating; and
3) capability of quickly neutralizing the electric charges when the photoconductor receives light rays.
Each of the above photoconductors has other superior properties and drawbacks on the practical use as well as these basic properties, respectively. However, an organic photoconductor has been remarkably developed for a couple of years, since it is manufactured with low cost, and it hardly contaminates the environment, and further it can be designed rather free.
Generally, there are two kinds of organic photoconductors; organic photoconductors of single-layer type and organic photoconductors of lamination type. The organic photoconductor of single-layer type itself functions to generate electric charges and to transport the generated electric charges. On the other hand, the organic photoconductor of lamination type consists of a charge carrier generation layer (CGL) functioning to generate electric charges and a charge carrier transport layer (CTL) functioning to transport the electric charges generated in the charge carrier generation layer. If necessary, an organic photoconductor may be provided with a blocking layer between the organic photoconductor and a conductive substrate in order to prevent electric charges in the conductive substrate from entering the organic photoconductor or to prevent light from being reflected by a conductive substrate provided under the organic photoconductor.
These organic photoconductors have superior properties as mentioned above. However, since such organic photoconductors have low hardness, they are easily worn or scratched by developers, cleaning parts, or the like during copying process.
Due to the wear of the organic photoconductor, electric potential of the organic photoconductor surface is decreased. and the local scratches on photoconductor are copied on a copying sheet. These two drawbacks largely influence a photoconductor's life.
In order to solve these drawbacks, a method of protecting surfaces of organic photoconductors has been proposed. In this method, a protective layer is disposed on the surface, whereby durability of organic photoconductor against mechanical loads which photoconductor receives internally or externally from copying machines has been improved.
Concerning methods to improve durability of organic photoconductors, for instance, a method of providing an organic film on a surface of photoconductor (as described in Japanese Patent Publication No. sho38-15446), a method of providing inorganic oxide (as described in Japanese Patent Publication No. sho43-14517), a method of providing an adhesive layer and subsequently an insulating layer (as described in Japanese Patent Publication No. sho43-27591), a method of providing an a-Si layer, a-Si:N:H layer, a-Si:O:H layer, or the like by means of plasma CVD method or photo CVD method (as described in Japanese Patent Provisional Publication Nos. sho57-179859 and sho59-58437), and the like have been proposed. Further a diamond like carbon film having high hardness have been utilized as a protective layer provided on an organic photoconductor for a couple of years. A protective layer made from amorphous carbon or hard carbon provided on a photoconductive layer (as described in Japanese Patent Provisional Publication No. sho60-249155), a protective layer made from diamond like carbon provided on a photoconductor surface (as described in Japanese Patent Provisional Publication No. sho61-255352), an insulating layer having high hardness containing carbon as a main ingredient provided on a photoconductive layer (as described in Japanese Patent Provisional Publication No. sho61-264355), a protective layer consisting of plasma organic polymer layer containing at least atoms such as nitrogen atoms and alkali metal atoms which is provided on an organic photoconductive layer (as described in Japanese Patent Provisional Publication Nos. sho63-97961 to sho63-97964), a protective layer consisting of amorphous hydrocarbon layer containing at least atoms such as chalcogen atoms, atoms in group III in the Periodic Table, atoms in group IV in the Periodic Table, and atoms in group V in the Periodic Table generated by glow discharge which is provided on an organic photoconductive layer (as described in Japanese Patent Provisional Publication Nos. sho63-220166 to sho63-220169), and the like have been proposed as examples of protective layer.
In every proposition mentioned above, a thin layer having high hardness containing only carbon or carbon as a main ingredient (belonging to a group of so-called i-carbon layer or diamond like carbon layer) is formed on a surface of an organic photoconductive layer by means of ion processing such as sputtering method, plasma CVD method, glow discharge method, and photo CVD method.
By providing the protective layers, hardness of organic photoconductor surfaces was raised. However, such hard surfaces of the protective layers are immune to wear, so that hollows formed on surfaces of protective layers by virtue of hollows such as pinholes or cracks existing on the surfaces of the organic photoconductive layers remain and the surfaces of the formed protective layers do not become even. In such hollows are gathered foreign matters which lower resistance of photoconductor surfaces, whereby image flow is caused.
When resistance of photoconductor surfaces is lowered by the foreign matters, electric charges which the photoconductor surfaces should be charged with before the photoconductors are exposed to light move easily. Hereupon, latent images become blurred and consequently blurred images which seen to be flowing are obtained on a copying sheet. This is called image flow. Foreign matters such as nitrogen oxides generated by corona discharge, phosphorus oxides contained in toner, and the like react on moisture in the air and are ionized. And the ions generated at this moment such as nitric acid ions, sulfate ions, ammonium ions, and hydroxly group ions and protons act as electric charge transport carriers, and due to such carriers resistance of photoconductor surfaces is lowered. The presence of these foreign matters has been known before the propositions of providing hard protective layers on the photoconductor surfaces. However, because soft surfaces of photoconductors wear while developing with toner, transferring, cleaning by means of cleaning blade or squeegee, these foreign matters gathering in hollows are removed together, so that the presence of the foreign matters was not a problem.
However, in the case where a protective layer 33 having a high hardness is provided on the organic photoconductive layer 30, hollows 34 such as pinholes and cracks are formed in the protective layer 33 as shown in FIG. 9 and the hollows 34 are not reduced by abrasion because of the high hardness of the protective layer 33. Therefore, foreign matters such as ions continue to be collected in the hollows 34 and keep resistance of the photoconductor surface small near the hollows 34. Owing to the small resistance, image flow, blur of images, and the like are formed in a copy.